The present invention generally relates to a direct current (DC) electrical arc furnace, and in particular to a bottom electrode of a DC electrical arc furnace.
Electrical arc furnaces have been widely used in refining metals, especially steel. Generally speaking, an electrical arc furnace takes the advantage of opposite electrodes arranged on top and bottom of a vessel to generate electrical arcs for melting raw material of metal disposed in the vessel. An example of the electrical arc furnace is disclosed in U.S. Pat. No. 5,191,592 issued on Mar. 2, 1993 to Robert A. Janiak and Nicolas Meysson and assigned to Clecim. FIG. 1 of the attached drawings shows the general structure of an electrical arc furnace. The electric arc furnace comprises a vessel 10, a top electrode 12 arranged on the top of the vessel 10 and several bottom electrodes 14 fixed to and extending through a bottom lid 16 of the vessel 10. The electrodes 12, 14 are connected to a power source, such as an electric main, for generating electric arc therebetween to melt the raw materials of metal disposed in the vessel 10.
FIG. 9 shows conventional bottom electrodes 14 mounted to the bottom lid 16 of the vessel 10. The bottom lid 16 defines a plurality of through holes 20 in which the bottom electrodes 14 are received. Each bottom electrode 14 has mounting means 22 for being mounted to the bottom lid 16 by bolts 24. The bottom lid 16 is attached to a bottom opening 28 of the vessel 10 by means of fastening pins 26 whereby the bottom electrodes 14 are partially inserted into the vessel 10.
Referring to FIGS. 10-12, each bottom electrode 14 comprises an elongate electrode body 30. The mounting means 22 comprises a circumferential flange 32 extending from a lower portion of the electrode body 30. A ring connection member 34 is positioned on the circumferential flange 32 and fixed thereto by bolts 36. The ring connection member 34 has an inside diameter substantially greater than an outside diameter of the electrode body 30 thereby defining a ring space 38 therebetween. The ring connection member 34 defines a plurality of holes 40 for receiving the bolts 24 that secure the ring connection member 34 to the bottom lid 16. The ring connection member 34 has an outside diameter greater than an inside diameter of the corresponding hole 20 of the bottom lid 16 for completely closing the hole 20.
A first insulation ring 42 is interposed between the bottom lid 16 of the vessel 10 and the ring connection member 34 and a second insulation ring 44 is interposed between the ring connection member 34 and the circumferential flange 32 of the bottom electrode 14 for electrically isolating the bottom electrode 14 from the vessel 10. An insulation collar 46 is fixed to the inside diameter of the ring connection member 34.
On the bottom lid 16 of the vessel 10, refractory material 48 in powder form are disposed as shown in FIGS. 12 and 13 for protection of the vessel 10. During the refining process, heavy metal impurity, such as lead, is molten and penetrates through the refractory powders 48 and sinks toward the bottom lid 16 as shown by curved lines of FIG. 13. Drainage holes 49 are defined in the bottom lid 16 through which the impurity flows out of the vessel 10. Conventionally, the impurity that flows out of the vessel 10 through the drainage holes 49 is not properly guided and may get contact with the bottom electrodes 14. Since the molten metal inside the vessel 10 and the bottom electrodes 14 are in general not in the same electrical potential, the contact therebetween causes a short-circuiting resulting in damage to the furnace thereby reducing the service life thereof and increasing the overall costs. The electric arc furnace disclosed in Clecim patent has to be inspected after 1500 batches and the bottom electrodes 14 have to changed. This causes an increase of costs.
Thus, it is desired to provide a bottom electrode of electric arc furnace in order to overcome the problems discussed above.
Accordingly, an object of the present invention is to provide a bottom electrode of an electric arc furnace comprising impurity guide means for properly guiding the impurity flowing out of the furnace without contacting the bottom electrode thereby eliminating short-circuiting problem and reducing the costs.
Another object of the present invention is to provide a bottom electrode of an electric arc furnace, which has an extended service life thereby reducing the overall costs.
To achieve the above object, in accordance with the present invention, there is provided a bottom electrode of a direct current electric arc furnace comprising an electrode body extending through a hole defined in a bottom of the furnace. A circumferential flange is formed around a lower portion of the electrode body to which a ring connection member is attached. The connection member forms a ring channel defined by inner and outer walls from which inner and outer flanges radially extend in opposite directions. The inner flange is fixed to the circumferential flange of the electrode body by bolts. The outer flange is fixed to the furnace bottom for attaching the bottom electrode to the furnace bottom. The channel is located between the circumferential flange of the electrode body and an inside diameter of the hole defined in the furnace bottom for increasing radial distance between the electrode body and the hole of the furnace bottom. Insulative members are arranged on and under the circumferential flange of the electrode body for electrically isolating the electrode from the furnace bottom.